Removal Of Heavy Metals In Smeltery Waste Water By Absorption With Modified Bentonite

A variety of heavy metals ions and its compound have been produced in thesmelting process. These pullutions are great harm to the environment and the urgentneed will be to develop effective treatment of heavy metal pollution. Bentonite is akind of natural clay mineral, which is low cost and has effective adsorptionperformance. Though modificating and regulating the interlayer and structure of thebentonite, its adsorption performance can be improved efficively. Therefore, theapplied efficient adsoption material and treatment tenique will be important in thetreatment of smelting wastewater.At the same time, the separation of solid and liquid is difficult, the presence ofthese problems restricted the application in heavy metal wastewater treatment. As aresult, modificating and regulating the interlayer and structure of the bentonite, toimprove the adsorption performance of bentonite, and effective adsorption treatmentwastewater containing a variety of heavy metal smelting, bentonite in the practicalapplication of wastewater treatment will be more extensive.This paper adopts the sulfuric acid, high temperature roasting and microwaveModified Bentonite (MB) method to produce three kinds of MB. Cadmium and Leadwere seleted for representives of heavy metals. The effect of modification methodsand process conditions of modified bentonite in adsorbing heavy metals was studiedand then the best modification methods were optimized. Base on these results, theoptimization conditions were investigated. To accelerate the separation of MB andimprove its adsorption efficicency, combined tenique with the microwave MB andPAM was researched to treat heavy metals in actual waste water. Also theoptimization conditions were investigated using the microwave MB and PAM. Fromthe results of XRD, FT–IR and SEM, the interlayer structure and surface propertiesof MB were discussed to explore the adsorption mechanism. The results could belisted as follows:(1) Compared with original soil, microwave MB or high temperature calcinatedMB has a better adsorption performance. Under the best condition (pH=8, T=40min,and the dosage the microwave MB with7min activation was20g/L), the removal rateof Cd2+and Pb2+could reach99.2%and95.3%respectively. Similarly when hightemperature calcinated MB with450℃calcination was20g/L, pH was9and adsorption time was40min. Cd2+and Pb2+removal rate could reach99.8%and99.8%respectively. And the energy costs of microwave MB and high temperaturecalcinated MB were0.1and8.8yuan/kg soil, respectively. Therefore, microwaveactivation MB was more application prospects than high temperature calcinated MBdid in application of Cd2+and Pb2+wastewater treatment.(2) When microwave MB dosage was25g/L, pH value was8, adsorption timewas50min, the removal manganese, zinc, cadmium and lead can only reach88.8%、92.6%、89.6%and94.3%in dealing with actual smelting waste water. However, itstill can’t meet the emissions standard of pollutants for lead and zinc industy in China（GB25466-2010）.(3) When microwave MB dosage was25g/L, PAM dosage was2mg/L, pHvalue was8, adsorption time was50min, the removal of manganese, zinc, cadmiumand lead can reach98.9%,99.6%,98.9%and99.6%respectively and it can meet theemissions standard of pollutants for lead and zinc industy（GB25466-2010）.Furthermore, a better separation performance was found in combied tenique withmicrowave activation MB and PAM.(4) The adsorption process of Cd2+and Pb2+by microwave MB was accordedwith Langmuir equation. The control power of internal diffusion was larger thanliquid membrane. From XRD, FT-IR and SEM analysis of MB before and afteradsorption, bentonite adsorption mechanism was ion exchange, surface adsorptionand the crystal layer.